192 ELECTRIC RAILWAY ENGINEERING small amount of ignition mixture, will react as above explained with sufficient heat to melt the iron which in turn is poured about the rail ends. This produces a joint similar to the cast weld with less metal but with apparently quite as good electrical and mechanical characteristics. Electric Welded Joint.—In contrast to the electric welded bond mentioned above there may be found in the' city tracks of many railway companies the electric welded rail joint. This, a rigid rail joint produced by electrically welding heavy iron bars 1 Ac. Side "Rotary Do. Side Kotary Special Current- Transformer Counooted to Bond Clamps PKL 73.—Connections for electric welding of bonds. on cither side of the webs of adjacent rail ends, should be carefully differentiated from the electric welded bond, although the proc- ess of welding is almost identical with that outlined above, with the exception that iron only is used and the size of weld and corre- sponding power used are much greater. In this latter type of joint, iron filler blocks are inserted between the rail ends and ground to the form of the rail head so that the joint is entirely closed and the operation of cars over rail joints is made so much the smoother. This j oint has given very satisfactory service both electrically as a bond, for its conductivity is practically equal to